Hugh and Jemima's £18m home

A top City financier told today how he had sold his Chelsea house to Hugh Grant and Jemima Khan for £18 million.

The couple, who are at the centre of mounting wedding speculation, are to move into the property in August.

James Arbib confirmed the sale of his house, where he has lived for the past eight years. He bought it when it was badly run down and has since spent more than £1.5 million on a series of improvements.

Mr Arbib is the son of fund management tycoon Sir Martyn Arbib, who has spent his fortune on racing and substantial donations to the Conservative Party.

He was knighted after supporting plans for one of Tony Blair's controversial city academies in Slough and this year alone has donated £100,000 to the Conservatives.

The sale of the house makes it the most expensive property per square foot sold in London.

The 6,000 square feet building, in a square in Chelsea, has a quarter acre of gardens, three garages and nine bedrooms and retains much of its original decor from 1934, when it was completed by architect Oliver Hill. But the property, which was awarded a Grade II* listing in 1998, has also been extensively modernised in recent years.

Sir Martyn was valued at £370 million in the Sunday Times Rich List 2006, making his family the 170th wealthiest in the country.

He made his fortune through Perpetual, a fund management company he set up with two phones and a secretary. It was sold for £1.05 billion in 2000, with Sir Martyn taking £113 million in cash and £200 million in shares.

James Arbib, 35, owns 4 per cent of Queen's Park Rangers football club and along with many of the family, has inherited his father's love of racing.

The Chelsea deal will end a difficult period of house-hunting for Ms Khan, 32, and Grant, 45.

Ms Khan, heiress daughter of the late billionaire Sir James Goldsmith, recently had a £15 million bid for a house in Barnes refused. The couple had been believed to be looking in Richmond, near the home of Ms Khan's mother, Lady Annabel Goldsmith.